Probably one of the most important aspects of body language is facial expression.
People subconsciously make and process and enormous amount of facial expressions. This is incredible powerful stuff I've your able to master it.
There is training material to help you to recognize these facial expressions that are normally only processed subconsciously. For example the stuff from Dr. Paul Ekman.
What would be even more useful is if it's possible to train your own micro facial expressions to convey the message you want.
Does anyone have any information on this?

One of the ideas that has helped me tremendously is to relax. Release the tension in every single muscle in your face. don't try to force any kind of facial expression.

When your face appears relaxed (along with the rest of your body), people will be more comfortable around you.

Check out Lie To Me at fox.com
It's TV show about micro facial expressions. Its awesome and that episodes are all there for free!